Patent GB-1118531-A (GB)
Title: Improvements relating to mechanical gear train assemblies
Inventor: MORFEY DENNIS SURRIDGE
IPC: F16H37/00
Filed: 1963-11-14
Abstract: 1,118,531. Change-speed control. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. 13 Jan., 1965 [14 Nov., 1963], No. 45047/63. Headings F2D and F2U. A variable-ratio gear particularly for the drive of a potentiometer causing the temperature of a nuclear reactor to rise at two controlled rates in sequence, includes a two-speed gear such that for forward drive initially an output shaft is driven at high speed for a predetermined angular rotation whereafter a fast drive shaft is automatically arrested and the output is driven at low speed. As shown an output shaft 1B is driven from a shaft 4 either at high speed through a gear 20 meshing a gear 17 connected to a shaft 1A by a friction slip clutch 24, the shaft 1A being connected to the output shaft 1B by a lost-motion coupling 30 and a spiral spring 28 arranged in parallel, or at slow speed by a gear 19 fast on the shaft 4 meshing a gear 18 connected to the output shaft 1B by a one-way coil-spring coupling 32. In operation for forward drive initially drive is at high speed through gears 20, 17, slip clutch 24 and shaft 1A and thence through the lost-motion coupling 30 which is biased by the spring 28 so that the lost-motion is taken up, to the output shaft 1B. The shaft 1A is connected by a lost-motion coupling 26 to a finger 37 co-operating with a stop 38. Both lost-motion couplings comprise a series of discs having pins engaging slots in the adjacent disc. Thus after a predetermined angular rotation of shaft 1A the lost-motion in coupling 26 is taken up and the finger 37 is rotated until it abuts stop 38 whereupon the shaft 1A is stationed and the clutch 24 slips. Thereafter drive is by way of gears 19, 18 and the clutch 32. This rotation of the output shaft is permitted by the lost motion of the coupling 30, the spring 28 being wound up by this rotation, and the rotation is limited by a further lost-motion coupling 22 having an arm 41 co-operating with a micro-switch 43 and a stop 42 such that when the lost-motion is taken up the micro-switch is engaged to stop a driving electric motor 1 and the stop 42 arrests the output shaft 1B in the event of failure of the micro-switch. The motor 1 drives through a reduction gear 3 a shaft 2 having a gear 5 meshing teeth of a planet carrier 6 of a planetary gear having planets 8, 9 meshing sun gears 10, 11 which are respectively fast on the shaft 4 and loose thereon, a sprag 15 being frictionally connected to the shaft 2 and on forward rotation thereof engaging, after some idle movement, the sun gear 11 to station it so that the gear 10 is driven and the shaft 4 drives the output shaft 1B. For reverse drive of the output shaft motor 1 is reversed, sprag 15 is removed from the gear 11 and the planet carrier 6 is clutched to the shaft 4 by a one-way clutch 39 so that shaft 4 is driven in reverse at high speed. Gear wheel 18 is thus driven and during the first stage of reverse drive the spring 28 which tends to turn the shaft 1B in reverse keeps the one-way clutch 32 engaged. The spring 28 also prevents the shaft 1A from being rotated. During this stage of reverse drive the spring 28 drives the shaft 1B at a speed controlled by the gearing. When the lost-motion of the coupling 30 is taken up, the shaft 1A is driven through the gear 17 and clutch 24 and drive is transmitted to the shaft 1B through spring 28 which keeps the one-way clutch 32 engaged so that the clutch 24 slips and the reverse drive speed is thus controlled throughout by the gears 18, 19. The gear 19 is connected to the shaft 4 by a slip clutch 21 which acts as a safety device to prevent damage in the event of micro-switch 43 failing to operate.